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University of Southern California Dissertations and Theses
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The long-term cephalometric and respiratory outcomes of mandibular distraction osteogenesis in infants with Pierre Robin sequence
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The long-term cephalometric and respiratory outcomes of mandibular distraction osteogenesis in infants with Pierre Robin sequence
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Content
The long-term cephalometric and respiratory outcomes of mandibular distraction
osteogenesis in infants with Pierre Robin Sequence
by
Tamara N. Shamlian
A Thesis Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA In
Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)
May 2015
Tamara N. Shamlian
2
Table of Contents
I. Abstract 3
II. Introduction 5
III. Literature Review 7
1. Pierre Robin Sequence 7
2. Craniofacial Microsomia 9
3. Treacher Collins Syndrome 12
4. Cleft Palate 13
5. Airway Management 14
6. Tracheostomy 16
7. Mandibular Distraction Osteogenesis 19
IV. Patients and Methods 24
1. Sample
2.Method
3.Validation
V. Results 28
VI. Discussion 31
VII. Conclusion 36
VIII. Bibliography 37
IX. Appendix of Charts and Figures 44
3
I. Abstract
Background
Micrognathia presents in many craniofacial disorders and may have immediate and long-term
effects on the neonatal airway. Airway obstruction is a critical condition that often requires
immediate intervention—ranging from intubation to tracheostomy, and mandibular distraction
osteogenesis.
Objectives
1) Evaluate long-term development—assessed by cephalometrics analysis—of Pierre Robin
Sequence (PRS) patients that underwent mandibular distraction osteogenesis (MDO) to alleviate
airway obstruction. 2) Identify changes in growth patterns in this patient population as compared
to published age-matched norms and age-matched untreated PRS patients. 3) Identify respiratory
changes through polysomnography.
Patients and Methods
A retrospective chart review and analysis was performed following approval of the Institutional
Review Board (IRB). The sample consisted of 12 non-syndromic PRS patients diagnosed with
respiratory distress or respiratory failure (based on polysomnography data) that had undergone
mandibular distraction osteogenesis at Children’s Hospital Los Angeles (Los Angeles, Calif.)
PSG was performed to document any changes in status of the breathing disorder. Lateral
cephalograms were taken and digitally traced using a Bjork analyses and USCF Cranio analysis,
and growth comparisons were produced.
Results
There was a statistically significant increase in gonial angle (ML/RL) of the Pierre Robin
sequence patients treated with MDO (PRSMDO) compared to untreated PRS patients. The
4
mandibular ramus length (Ar-GO) was significantly shorter, and mandibular body (Go-Gn) was
significantly longer in PRSMDO patients. Chin prominence (SN-Pg) was greater in PRSMDO
patients. Maxillomandibular sagittal relationship (ANB) in the tested sample had a statistically
significant closer approximation. Upper face height (N-ANS), lower face height (ANS-Gn),
maxillary length (Co-A), and mandibular length (Co-Gn) were all shorter with statistical
significance. All other measurements showed no statistical significance.
Conclusion
The candidates for early intervention with MDO represent the most severe micrognathia cases.
Further study of these patients is needed to determine if the more vertical growth vector observed
in these patients will lead to a dolichofacial profile as the patient matures. Should an extremely
high gonial angle lead to an anterior skeletal and dental open bite paired with a non-pleasing soft
tissue profile, these patients—once skeletally mature—may require two-jaw orthognathic surgery
to address their facial disharmony.
5
II. Introduction
Micrognathia is the craniofacial anomaly of a small and retrusive mandible, which may have
immediate and long-term effects on the neonatal airway. It is found in a multitude of diagnoses,
ranging from craniofacial microsomia to nonsyndromic Pierre Robin Sequence, and is
representative in many syndromes such as Treacher Collins, Cri du chat, and Marfan syndrome.
While the inheritance pattern varies between these conditions, a universal step-wise approach is
used in diagnosing micrognathia. A multidisciplinary team should evaluate all patients with
micrognathia, to fully assess the maxillary-mandibular relationship, anatomically define the site
of airway obstruction, and identify feeding difficulties. Patients should be evaluated for episodes
of desaturation that occur spontaneously, during feeding, or during sleeping. Furthermore,
patients that experience desaturation should be evaluated with double endoscopy –
nasoendoscopy and bronchoscopy (Schaefer et al., 2004). If the airway obstruction is localized to
the tongue base alone and cannot be controlled with conservative measures, then tongue-lip
adhesion is the initial treatment of choice. If this is not sufficient, a surgical treatment option
must be selected, though there is currently controversy on this topic (Mackay, 2011; Jarrahy,
2012).
Airway obstruction is a sequela of mandibular micrognathia, and may require immediate
intervention ranging from intubation to tracheostomy, and mandibular distraction osteogenesis
(MDO). Historically, mandibular distraction among neonates has been reserved for failures of
tongue-lip adhesion in which isolated tongue-base airway obstruction is documented. The
argument for avoiding routine distraction is that complications of facial scarring, nerve and tooth
bud injury, and potential disturbances of intrinsic mandibular growth should be avoided
(Schaefer, et al., 2004). Tracheostomy has been the standard of care for these neonates, but in
6
addition to leaving a visible scar in the neck, requires 24-hour managed care by an adult. Having
a caregiver present at all times has been shown to impact the psychosocial development of these
children, and has financial, emotional and psychological ramifications for the caregiver. A less
onerous option—though equally technique sensitive—is MDO, which serves to correct the
skeletal deformity in addition to the airway obstruction. With ever-increasing technology and
improvements in medical devices, MDO will soon overcome many of its previous complications.
The aim of this study was to determine the long-term growth outcomes of early intervention with
MDO in patients with Pierre Robin Sequence (PRS) by evaluating cephalograms. Additionally,
changes in respiration were evaluated with polysomnograms. Findings were compared to age-
matched norms and age-matched patients with untreated PRS from the literature (Suri et al.,
2010).
7
III. Literature Review
1. Pierre Robin Sequence
The triad of micrognathia, glossoptosis, and airway obstruction—with or without cleft palate—
characteristic of Pierre Robin syndrome was first diagnosed by the French stomatologist, Pierre
Robin, in 1923. The name was later changed to Pierre Robin sequence (PRS), as this term better
represents the pattern in which multiple anomalies are initiated sequentially from a single prior
anomaly. PRS has a reported prevalence ranging from 1 in 8,500 to 1 in 20,000 births (Bush et
al., 1983; Tolarova et al. 1998). It has been described to be heterogeneous and pathogenetically
and phenotypically variable (Suri et al., 2010). The primary defect or malformation is
mandibular micrognathia between 7-11 weeks in utero (Figueroa et al., 1991). The small or
retruded mandible maintains the tongue in an elevated and retruded position into the lower
posterior pharyngeal space (glossoptosis) leading to a tertiary disruption in the fusion of the
palatal shelves (Shen et al., 2012). A U-shaped cleft palate is the result in the majority of PRS
patients. The literature reports that 84.5-95% of these patients exhibit a cleft palate (Carey et al.,
1982; Anderson et al., 2011; van Lieshout et al. 2014). The anatomy of a PRS patient’s mandible
and their tongue position can lead to airway obstruction and feeding difficulties (Matsuda et al.,
2006). See figure 1.
Research has shown that there are several mechanisms of airway obstruction in PRS patients.
True glossoptosis occurs when the tongue is in contact with the posterior pharyngeal wall. The
tongue’s contact with the soft palate, medial collapse of the lateral pharyngeal walls, and
sphincteric constriction of the pharynx can all manifest as airway obstruction (Olson et al.,
2011). Consequences of airway obstruction range from hypoxia to cor pulmonale, failure to
thrive, and cerebral impairment. Addressing the airway problem may require (in order of
8
increasing invasiveness) prone positioning, placement of a nasopharyngeal tube , tongue-lip
adhesion, mandibular distraction, and tracheostomy (Sher et al., 1992; Myer et al., 1998; Denny
et al., 2004; Dauria et al., 2008; Meyer et al., 2008). Evans et al. found that 42% of their patients
with PRS required feeding tube insertion to correct feeding difficulties (2006). Anderson et al.
showed that 85% of infants suffered from obstructive sleep apnea (2011). Patients with PRS that
have respiratory airway obstruction can often be managed with conservative measures such as
prone positioning or nasopharyngeal tubes with a success rate of 45-69.2% (Caouette-Laberge et
al., 1994; Kirschner et al., 2003). Smith et al. found that 28% of patients with isolated PRS
required intervention beyond positioning to address airway obstruction (2006).
1.1. Skeletal growth pattern of Pierre Robin Sequence Patients
Different facial types have been identified in PRS patients. Compared to age-matched norms,
Shen et al. (2012) found that their PRS sample had shorter cranial base lengths, and shorter
maxillary and mandibular lengths. Suri et al (2010) concluded that children born with Pierre
Robin sequence have smaller cranial bases, bimaxillary retrognathism and smaller maxillae and
mandibles than age matched norms when assessed at a prepubertal age of 11.7. These patients
also exhibit steeper planes of the maxilla and mandible. Their growth patterns are more vertical,
with backward mandibular growth rotation leading to increased anterior face height. This result
does not improve through puberty with “catch-up growth” (Roberts et al. 1975; McCarthy et al.
1999; Hermann et al., 2003). According to Shen et al. (2012), PRS patients present with
hypodontia of permanent lateral incisors to premolars (up to 36%). Missing posterior teeth,
arrested development, and class III to normal class I malocclusions are common in this
population of patients receiving MDO.
9
2. Craniofacial microsomia
Craniofacial microsomia (CFM) is the second most common congenital syndrome of the head
and neck with an incidence of 1:3,500 live births (Kusnoto et al., 1999). Patients with
craniofacial microsomia may benefit from mandibular distraction to improve their facial
asymmetry and alleviate airway problems. CFM is part of the oculo-auriculo-vertebral spectrum
of disorders, but has no evidence of genetic transmission. The incidence of bilateral involvement
is reported in 10-15% of cases with one side displaying more severe expression. The degree of
hypoplasia can be variably in any of the structures derived from the first and second brachial
arches. Involved structures include the jaws, other skeletal components, muscles of mastication,
ears, nervous system, and soft tissue (Pruzansky, 1969; Roberts et al., 1975; Poswillo, 1988). See
Table 1.
A study by Kusnoto et al. (1999) analyzed growth patterns of patients with hemifacial
microsomia (HFM) who underwent mandibular distraction osteogenesis on the affected side. In
the comparison group, for a period of 8 years on the affected side, the ramus height, body length,
and total mandibular length increased at an average rate of 1.3, 1.9, and 3.0 mm, respectively,
per year. On the unaffected side, the ramus height increased by 2.1 mm per year; the mandibular
body increased 1.9 mm; and the total mandibular length increased by 2.9 mm per year. The
average pattern observed included: 1) the gonial angle on the affected side was increased by 1°
per year, yet decreased by 1°per year on the unaffected side; 2) the proportions between the
affected to the unaffected side were maintained; 3) in the 6 individuals eighteen months after
MDO, it was found that the ramus height was reduced by 1.0 mm, whereas the body was found
to resume its growth with a faster rate on the distracted side, maintaining its proportion; 4)
angular changes demonstrated closing of the gonial angle on both the unaffected (0.5°) and
10
distracted (3.5°) sides. Three-dimensional observations were the following: 1) on average,
unoperated patients with isolated HFM tend to maintain their asymmetrical facial proportions
and do not worsen substantially with time; 2) different treatment effects were seen on the ramus,
body, and total length of the mandible: changes in body length > ramus height > total length; 3)
eighteen months after MDO, the correction was stable but with some degree of settling back
from the initial overcorrection (< 5%); 4) eighteen months after MDO the mandibular body was
found to have greater growth than the ramus (Kusnoto, et al., 1999). See figure 2.
Craniofacial microsomia can be classified by the OMENS classification, and the Pruzansky
classification scheme. A nosologic system, presented by Vento, et al. (1991), utilizes the
acronym O.M.E.N.S. to highlight five major dysmorphic manifestations of hemifacial
microsomia (HFM). The system uses “O” for orbital distortion; “M” for mandibular hypoplasia;
“E” for ear anomaly; “N” for nerve involvement; and “S” for soft tissue deficiency. The OMENS
system is easily adapted for data storage, retrieval, and statistical analysis.
Prusansky correlated the degree of mandible development with ear anomalies in 90 patients,
based upon the ear classification described by Meurman. (Pruzansky, 1969). The classification
system is outlined below:
Pruzansky type I: the mandible is small with normal shape and morphology.
Pruzansky type II: the condyle, ramus and sigmoid notch are present but distorted in size and
shape; the mandible is different from the norm in size and shape with a functioning TMJ and
glenoid fossa.
Pruzansky type III: there is a complete absence of ramus and glenoid fossa on the affected side
with no mandibular development posterior to the dental follicles.
11
Mulliken and Kaban (1987) found that Pruzansky’s system had two weaknesses: it was possible
to have a Pruzansky II with a functioning TMJ, but with or without a zygomatic arch and glenoid
fossa, and it was possible to have a Pruzansky III with no condyle and no functioning TMJ, with
or without a zygomatic arch and a glenoid fossa. The categories for CFM were modified thus:
Type I: the condyle and ramus are reduced in size but the overall morphology is maintained.
Type IIa: the ramus and condyle demonstrate abnormal morphology but the glenoid fossa has
maintained a position in the temporal bone similar to that of the contralateral side.
Type IIb: the ramus and/or condyle are hypoplastic, malformed, and displaced outside the
plane of that of the contralateral side.
Type III: the ramus is essentially absent.
Three-dimensional cone beam commuted tomography (CBCT) enables classification of this
condition with better accuracy. See figure set 3
12
3. Treacher Collins Syndrome
Treacher Collins syndrome, or mandibulofacial dysostosis, was first reported by Thomson in
1846, but has been associated with Treacher Collins, who described two cases in 1900. The
anatomical abnormalities associated with this syndrome include antimongoloid slanting
palpebral fissures (89%), malar hypoplasia with or without cleft in the zygomatic bone (81%),
mandibular hypoplasia (78%), lower lid coloboma, partial to total absence of lower eyelashes,
malformation of auricles, external ear canal defect, conductive deafness, visual loss, cleft palate
(28%), incompetent soft palate, and projection of scalp hair onto lateral cheek. Some occasional
abnormalities include but are not limited to pharyngeal hypoplasia, macrostomia, and
microstomia; and intellectual disability has only been reported in 5% of cases. This disorder has
an autosomal dominant inheritance pattern (Gorlin, 1999). Mutations in the gene TCOF1 are
responsible for close to 93% of cases. Two other genes, POLR1D and POLR1C account for
approximately 9% of cases with a wide variability in expression (Chung, et al., 2012).
Respiratory problems can arise due to a hypoplastic mandible and narrow airway, and may
require temporary tracheostomy.
Treacher Collins syndrome has some distinguishing features—absence of the medial lower
eyelashes and antegonial notching of the mandible—that are absent in craniofacial microsomia.
The facial profile in patients with Treacher Collins Syndrome has been described as “bird-like”
or “fish-like” due to severe mandibular retrognathia, which creates a high angle of convexity.
See figure 4. These patients exhibit normal anterior face height, but a markedly shorter posterior
face height (Roberts et al., 1975). The effective length of the mandible in these patients is also
reduced, with the direction of growth established early.
13
4. Cleft Palate
Some of the most common congenital birth defects include cleft lip and palate. Cleft palate can
occur as an isolated anomaly with an incidence of 1:2000 live births, or as part of a genetic
syndrome. Cleft palate is commonly seen in nonsyndromic PRS, while the most common
syndromic associations for cleft palate are Stickler syndrome (44%), velocardiofacial syndrome
(7%), craniofacial microsomia (3%), and Treacher Collins (5%) (Evans et al., 2006).
Three-dimensional imaging is a reliable way to assess airway volume. In a CBCT study of non-
syndromic cleft lip and palate (CLP) patients, Cheung et al. found that the most relevant
information can be obtained from axial images which are perpendicular to the direction of
airflow (2012). It has been published what individuals with CLP did not exhibit smaller total
airway volume than the norm.
In a study by Shen et al., isolated cleft lip and palate patients had a shorter cranial base, and
shorter mandibular length at a young age (4-7 years old), but the mandible and maxilla were
positioned similarly to the norm (2009). When a sample of patients ages 10-13 years of age was
evaluated the maxillary length was shorter and more retrusive, with mandibular length and
position being in line with the norm. This coincides with previous studies of cleft palate patients.
14
5. Airway management
Research and technology has improved diagnosis of micrognathia, and it is possible to identify
the defect in utero via ultrasound. An objective test involves measuring gestational age and
biparietal diameter, which are linearly correlated with mandibular growth. 100% sensitivity and
98.1% specificity have been reported with this method. Depending on the severity of the
deformity, a pulmonary specialist team will be present at delivery in the event that surgical
treatment is necessary.
According to Shen and Ward (2012), the pharyngeal structures must accommodate breathing,
feeding and speech which have different physical requirements. Breathing requires a rigid tube;
feeding needs a flexible tube to allow for peristaltic muscular movements; and speech requires
fine muscle and airway shape changes. The oropharynx is a carefully balanced system of
compromises among the different functions and it does not take much to destabilize this balance.
Upper airway stability is influenced by anatomical structure, neuromuscular activation of
muscles, ventilator control, and the arousal threshold from sleep (McCarthy et al., 2002). Initial
determination of airway quality requires measuring continuous pulse oximetry, carbon dioxide
levels on daily capillary blood gases, and the child’s ability to maintain adequate oral intake to
meet nutritional needs. Airway management is conservative at first (if possible) —repositioning
and instituting use of nasopharyngeal airways (Bath et al., 1997; Handley et al., 2013).
Polysomnography (sleep study) can measure REM, oxygen saturation, capnography, apneas,
hypopneas, and other values to provide insight into a child’s airway stability. See figure 6.
Congenital abnormalities of the airway, such as laryngomalacia, hemangiomas, pyriform
aperture stenosis, choanal atresia, and laryngeal webs may have effects on airway patency and
15
quality of respiration (McCarthy et al., 2002). Certain anatomical obstructions warrant treatment
with tracheostomy because MDO will not ameliorate the respiratory distress of the patient.
Significant risk factors for airway obstruction that will require surgery prior to age one include
prematurity (gestational age <37 weeks), prenatal ultrasound finding of intrauterine growth
restriction (IUGR), evidence of neurologic impairment, and a history of intubation in the first 24
hours of life (Handley et al., 2013). The result of pre-operative peripheral oxygen saturation of
about 40% or less in the prone position is considered an indication for surgery (Shen et al.,
2009).
16
6. Tracheostomy
When conservative measures such as glossopexy procedures, tongue-lip adhesions, or
subperiosteal release of the floor of the mouth fail to relieve a patient’s symptoms of apnea and
hypopnea, tracheostomy is a commonly used procedure to bypass the posterior pharynx (Cheng
et al., 2011). Historically, tracheostomy has been the standard of care in the management of
severe obstructive sleep apnea (OSA) attributed to micrognathia. Tracheostomy is a quick
therapy but has long lasting morbidity.
Tracheostomy was initially improvised by Armand Trousseau in order to treat diphtheria patients
exhibiting dyspnea (Itamoto et al., 2010). In the past, upper airway obstruction of infectious
origin necessitated that children undergo emergency tracheostomy. Presently, the main
indications for tracheostomy are upper airway obstruction (sometimes caused by craniofacial
malformations such as Pierre Robin sequence, craniofacial microsomia, Treacher Collins
syndrome), severe obstructive sleep apnea syndrome, prolonged orotracheal intubation (OTI),
subglottic stenosis, and laryngotracheal stenosis.
Tracheostomy on infants is a percutaneous procedure that is performed by a pediatric surgeon.
The neonate or infant is intubated under general anesthesia in the operating room and the
surgeon makes a vertical incision between the second and third tracheal rings. A tracheostomy
tube is placed and secured into position with nylon sutures and tracheotomy ties. A flexible
extension tube is used to connect the tube to a ventilator circuit immediately post-operatively
(Schlessel et al., 1993; Pereira et al., 2004). In children with hypotonia, developmental delay,
and neurological dysfunction, often tracheotomy and gastrostomy placement are more viable
17
options over MDO, because they also take into account poor coordination and chronic aspiration
(Denny et al., 2001; Katz et al., 2012).
6.1. Risks of Tracheotomy
Infant tracheostomy is wrought with a morbidity of 25%-50%, and perioperative mortality of
0.5% to 5.0% at major centers that perform these procedures (Miloro, 2010). In children, the
mortality associated with this procedure was found to range from 0.5-3% (Itamoto et al., 2010).
The mean age of patients that suffered complications in that particular study was 3.9 years.
Types of complications that arise immediately post-operatively, shortly thereafter or late post-
operatively include: cannula obstruction, accidental cannula loss, tracheocutaneous fistula,
tracheal stenosis, stoma granuloma or keloid formation, aspiration, and tracheomalacia. Less
common complications are: suture abscess, pneumomediastinum, bronchopneumonia,
pneumothorax, and innominate artery erosion (Rabuzzi et al., 1971; Sasaki et al., 1979; Singer et
al., 1989; C. Prescott, 1992; Sclessel et al., 1993; Pereira et al., 2004). Bacteriology after
tracheostomy is diverse, ranging from staphylococcus infections to Haemophilus influenza,
which often colonizes the cannulated respiratory tract (C. Prescott, 1992). A study by Pereira, et.
al (2004) documented complications of neonatal tracheostomy, concluding that meticulous
technique, surgeon experience, and post-operative specialized care could reduce the complication
rate.
6.2. Morbidity and quality of life issues
Negative sequelae of infant tracheostomy include failure to thrive, long and repeated
hospitalizations, delayed speech, and behavioral problems (Singer et al., 1989; Pereira et al.
2004). Though outcomes have improved over the years, there are high rates of moderate to
18
severe intellectual and physical impairments. Overall intellectual functioning of these children
has been recorded at the lower end of the average range in comparison with peers of similar age.
There is often a need for interdisciplinary programs for these children encompassing medical,
psychological, and rehabilitative services. Children that are tracheostomy-dependent must be
monitored at all times to ensure proper ventilation and airway patency.
Paes et al (2014) compared the direct and indirect costs and complications of conventional
tracheostomy to those of mandibular distraction osteogenesis. Evaluation of cost and
complications were obtained retrospectively from patient medical records and from a survey
completed by parents over a one-year period. They concluded that overall direct costs were 3
times higher for those that underwent tracheostomy when compared to the MDO group. The cost
for homecare and absence from work is a substantial downside of tracheostomy as are the
psychosocial issues faced by patients on ventilators.
Tracheostomy has been the standard of care for treating micrognathic infants with airway
obstruction. Recently, case reports and longitudinal studies evaluating MDO as an alternative
therapy for neonates and infants with respiratory distress due to micrognathia have been
documented (Hong et. al, 2011; Hammoudeh et al., 2012). PRS, Treacher Collins syndrome, and
other syndromes affecting the growth and development of the mandible are among the conditions
studied in these cases.
19
7. Mandibular Distraction Osteogenesis
Russian surgeon, Gabriel Ilizarov, is credited with demonstrating distraction osteogenesis of the
long bones. He theorized that a tension-stress effect would cause an increase in metabolic
activity, cellular proliferation, and neovascular ingrowth leading to bone lengthening.
The same scientific basis was applied by Snyder et al. in 1973. Several authors have described
the advantages of using distraction osteogenesis on the mandibles of neonates with obstructive
apnea in place of tracheostomy (Cohen et al., 1998; Denny et al., 2001; McCarthy et al., 2002;
Izadi et al., 2003; Wittenborn et al., 2004; Steinberg et al., 2005). Distraction osteogenesis of the
mandible in the human was first described by McCarthy et al. in 1992. The procedure involved a
surgeon making an osteotomy on the micrognathic mandible and attaching a distractor to both
sides of that osteotomy bilaterally (Muto et al., 2008).
The operative technique that had been used on the patients of the current study was described by
Hammoudeh et al in 2012. It involved a modified Risdon incision made 1 cm inferior to the
angle of the mandible, with the subperiosteal plane along the ramus and body of the mandible
and up to the coronoid process. The osteotomy was L-shaped with the horizontal plane parallel
with the inferior border of the mandible. The vertical component was made 1 cm anterior to the
posterior border of the mandible. Surgeons used a reciprocating saw to make a bicortical
osteotomy on the horizontal portion and the caudal part of the vertical component. A unicortical
osteotomy was made through the vertical component. See figure 7.
Internal Zurich microdistactors for use in neonates and infants (KLS Martin LP, Jacksonville,
FL) had been used on all patients. The distractors were placed nearly perpendicular to the
vertical component of the osteotomy so the distraction vector would be in the anterior direction.
The distractors were secured to the external surface of the mandible using self-tapping titanium
20
screws on either side of the osteotomy (Sadakah, et al., 2009; Farina et al., 2011). The osteotomy
was only then completed using an osteotome and a mallet. The activation arm of the distractor
was then passed through a subcutaneous tunnel posteriorly to the postauricular sulcus. The
submandibular incision was finally closed with resorbable sutures in layers (Hammoudeh et al.,
2012).
The distraction on these patients began one day following surgery at a rate of 1.5mm per day
(one turn every 8 hours). Distraction continued until the screw was fully extended (15-20mm).
Once activation was complete, the activation arms were removed in the operating room. After
the callus around the distraction site was allowed to consolidate for several weeks, a final
surgical procedure was done to remove the distraction device, and to revise the submandibular
scar.
MDO is comprised of three phases: latency, distraction and consolidation (Castano et al., 2001;
Yates et al., 2002; Glowacki et al., 2004; Cicchetti et al., 2012). According to a meta-analysis by
Ow et al. (2008), a 3-7 day latency period is most commonly used. Shorter latency periods are
more common for bilateral MDO, though a longer latency period is contributory to success.
White and Kenwright reported greater extraosseous circulation and bony deposition in the
lengthened rabbit tibia after a 7-day latency period compared to control without a latency period
(White et al., 1990).
An active distraction phase consisted of a rate of 1.0mm/day on average. The frequency of
activation varies from 2 to 4 times per day, with the more rapid rate preventing premature
consolidation during the distraction process. The histologic changes in the distraction sites
include 4 zones: central fibrous zone; transition zone (in which fibroblasts and undifferentiated
21
precursor cells are in continuity with osteoblasts); zone of bone remodeling with osteoclasts; and
mature bone zone showing compact cortical bone (McCarthy et al., 2002).
The consolidation period ranges from 6 to 8 weeks and callus maturation can be monitored using
ultrasonography and technetium-99 bone scanning (White et al. 1990). Longer consolidation
periods are beneficial for bone healing and maturation, but have morbidity associated with them.
Distraction osteogenesis is a bone-expanding technique in which bone is produced in response to
mechanical tension across an osteotomy similar to fracture repair. But, this process takes
advantage of controlled, iterative microtrauma and the mechanism of ossification is
intramembranous. Local growth factors that induce osteoblast proliferation, differentiation, and
activation are potential regulators of the processes of MDO. Yates (2001) and Franco (2010)
showed that new bone formed by direct membranous ossification due to increased expression of
growth factors TGF-β and BMP-4. Preservation of the periosteum through subperiosteal
dissection and the abundance of vasculature in the craniofacial skeleton are vital factors in rapid
healing and bone regeneration. Techniques for mandibular distraction include use of external,
internal, and resorbable, and uni- and multi-vectorial distraction devices. Though different tools
may be used, the concept is the same and can be performed on infants and adults (with no upper
age limit).
The MDO procedure treats the etiology of the upper airway compromise by lengthening the
mandible, advancing the base of the tongue away from the pharyngeal wall, elevating the hyoid
bone, enlarging the hypopharyngeal region (Miloro, 2010). MDO works like an expansion
appliance, gradually separating 2 segments of bone. The advancement of the tongue and floor of
the mouth increases the antero-posterior dimensions of the airway (McCarthy et al., 1992; Katz
et al., 2012).
22
To our knowledge, there have been no studies comparing the long-term craniofacial growth and
polysomnography outcomes of PRS patients treated with early intervention MDO with those of
non-MDO-treated PRS patients. The aim of this study was to analyze the craniofacial features
and mandibular morphology in patients with PRS treated with MDO (PRSMDO) and compare
our findings to age matched norms, and age-matched untreated patients with PRS from the
literature (Laitinen et al., 1992; Suri et al., 2010; Chung et al., 2012).
The five most commonly cited diagnoses that undergo bilateral MDO include Pierre Robin
sequence, class II mandibular hypoplasia, Treacher Collins syndrome, obstructive sleep apnea
and TMJ ankylosis (Ow et al., 2008). One author noted the indications for MDO: micrognathia
with a maxillomandibular discrepancy, over jet more than 8mm, repeated upper airway
symptoms with chronic low S
P
O
2
readings, repeated apnea monitor triggering, labored breathing
or cyanosis, poor oral intake, lack of weight gain consistent with age, abnormal sleep studies,
and direct laryngoscopy or flexible upper airway endoscopy showing obstruction at the tongue
base without significant laryngomalacia or tracheomalacia requiring tracheostomy (Miloro,
2002; Hammoudeh et al., 2012; Rachmiel et al., 2012).
The outcomes of MDO are generally predictable. There is reported improvement of asymmetry
and retrognathia, correction of slanted lip commissure, and leveling of the occlusal plane.
According to Ow et al. (2008), M DO prevented the need for tracheostomy in 91.3% of neonates
diagnosed with respiratory distress. Imaging studies have shown significant changes in the
antero-posterior and medio-lateral dimension of the supraglottic space from preoperative to early
postoperative time points (Rachmiel et al., 2005; Olson et al., 2011; Mohamed et al., 2011;
Cheung et al., 2012; Hong et al., 2012; Abramson et al., 2013). Commuted tomography (CT)
studies showed an increase in the A-P and transverse dimensions, increase in ramus height,
23
increase in mandibular body length, increase in the distance between the hyoid bone and the
posterior pharyngeal wall, and a correction of maxillomandibular alveolar ridge distances to an
average of 2mm in MDO patients(Mohamed et al., 2011). Additionally, micrognathic children
treated with distraction have improved outcomes in oral feeding with a relatively low rate of
long-term complications (Tibesar, et al., 2010).
7.1. Complications of Mandibular Distraction Osteogenesis
Mandibular distraction is safe, and the surgical scars are esthetically acceptable, but it does have
some complications. These include risks of damage to the inferior alveolar nerves, damage to
developing tooth buds, infections, failure of distraction, dislodgement of pins or distractors,
aspiration pneumonitis, premature consolidation of the bony regenerate, temporomandibular
joint dysfunction, joint ankylosis and potential growth restriction—but these are reported
infrequently (McCarthy et al., 2002; Miloro, 2010; Sesenna et al.,2012). Miloro reported their
most frequent complication following distraction as development of anterior open bite of the
occlusion or the alveolar ridges. They also reported that this side effect was resolved 3 months
after distraction device removal. Tibesar et al. studied 32 patients with micrognathia and
secondary airway obstruction that underwent MDO (2010). The complication of anterior open
bite was noted in this study as well with a prevalence of 28%. Five of 32 patients (16%) had
tooth malformation, tooth loss, or dentigerous cyst formation while an additional three patients
(9%) had long-term facial nerve injury from the placement of the distraction device. Most of
these complications can be resolved with subsequent orthodontic treatment, future orthognathic
surgery and dental restorations.
24
IV. Patients and Methods
This retrospective study was conducted at the Children’s Hospital Los Angeles (CHLA),
Department of Dentistry and Orthodontics, and Department of Plastic and Maxillofacial Surgery.
Institutional review board approval (IRB) was obtained by the USC committee on Human
Research and permission forms were signed by patients for participation. Data were collected
from the CHLA database using the diagnostic code for PRS. Individuals with complete medical
and radiographic records who had a confirmed clinical diagnosis of nonsyndromic PRS, or
another craniofacial disorder who had undergone mandibular distraction osteogenesis to alleviate
airway distress were included. All surgical procedures had been done previously by Drs. Mark
Urata and Jeffrey Hammoudeh of the Department of Plastic and Maxillofacial Surgery.
Individuals with syndromic association, tracheostomy, incomplete medical and radiographic
records, or who had expired post-operatively were excluded from this study. Of the 267
mandibular distraction procedures documented from 2003 to 2014, 80 were documented as
primary mandibular distraction osteogenesis (MDO) surgeries, during which the distraction
appliance was placed and activated. The study sample was further narrowed by excluding
patients receiving MDO for isolated hypoplasia or trauma. This yielded a total of 75 craniofacial
patients—33 of whom had PRS—whose families were contacted requesting that the patients
return for a follow-up visit. The initial patient sample that presented consisted of 12 patients with
non-syndromic PRS and 15 patients with other craniofacial syndromes. Patients had lateral
cephalograms taken to evaluate growth, and had polysomnography (PSG) done if indicated. All
patients had been initially treated at CHLA for respiratory distress or respiratory failure
diagnosed using PSG, pre- and post-operatively. All PSG had been performed in a sleep
laboratory with a daytime nap or overnight sleep study in a quiet darkened room. Standard
25
techniques were implemented and no sedation was used. The patients were observed
continuously by a PSG technician and behavioral observations were recorded in real time. All
data was collected and stored by a computerized PSG data acquisition system (Somnostar Pro 7-
3a; Somnostar/Cardinal Health, Dublin, OH, United States). Manual removal of artifacts was
performed and oxygen saturation data was subsequently tabulated. A board certified sleep
specialist scored the sleep staging and respiratory events according to the 2007 American
Academy of Sleep Medicine Criteria (Iber, 2007).
The obstructive AHI was calculated based on the number of obstructive apneas, mixed apneas
and hypopneas per hour of sleep. The patients were assessed by the pulmonary / critical care
team to rule out intrinsic pulmonary disease. An otolaryngologist also examined the patients to
rule out secondary lesions that could lead to airway obstruction such as tracheal malacia or
subglottic stenosis. All patients were examined by the Plastic and Maxillofacial Surgery team to
diagnose class II skeletal relationship and retrognathia or micrognathia. The respiratory distress
group included patients who had an abnormal apnea-hypopnea index (AHI) on PSG and had
failed initial conservative measures including prone positioning, oxygen supplementation and/or
watchful waiting.
All patients had been treated with MDO as infants (mean age: 2 months, 1 day; range: 14 days to
5 months, 1 day) as an alternative treatment to tracheostomy. The standard surgical protocol
described by Hammoudeh et al. was followed (2012). Children younger than age four and older
than age 18 at time of follow-up were excluded from the study. Based on availability of
published age-matched samples, only the 12 PRS patients were included in this study. See table
5. Age and sex were recorded at the time of radiographic acquisition. Pre-operative, post-
operative, and most recent PSG results were recorded to ensure that airway management by
26
surgical intervention with MDO had resulted in long-term elimination of the need for
tracheostomy.
Lateral cephalograms used in this study were taken in natural head position (utilizing a Sirona
Orthophos XG, model number D3352, Long Island City, United States) by an experienced dental
technician. Cephalograms were taken with lips relaxed and teeth in centric occlusion. As many
of these patients had difficulty with posturing in the cephalostat, natural head position did not
always coincide with true vertical line. 56 hard and soft tissue landmarks were digitized to form
a custom cephalometric analysis, which included landmarks and measurements from a Bjork
analysis, UCSF Cranio analysis and other analyses described by Laitinen et al., 1992, Suri et al.,
2010 and Chung et al., 2012. Tracings were completed by an orthodontic resident and verified by
a craniofacial orthodontic fellow using Dolphin imaging software (Version 11.5; Dolphin
Imaging and Management Solutions, Chatsworth, CA, United States). A total of 33 angular and
linear measurements were analyzed. A Bjork polygon analysis was performed on each of the
patients to determine dental and skeletal classification and mandibular growth vectors. See figure
8. UCSF Cranio analyses revealed measurements of interest that were later compared to
published age-matched norms and untreated PRS patients. The measurements of interest were
the sagittal mandibular length (Co-Gn), the sagittal maxillary length (Co-A), the sagittal position
of A point in relation to cranial base (SNA), and the sagittal position of B point in relation to
cranial base (SNB) and their differences (ANB).
Statistical Analysis
Cephalometric findings on PRSMDO patients were compared to published age-matched norms
and age-matched untreated PRS patients. This data was provided by University of California,
27
San Francisco faculty, Dr. Snehlata Oberoi, Associate Clinical Professor, Division of
Orthodontics, Department of Orofacial Sciences, and alumnus, Dr. Yoshi F. Shen. Their
research on “Facial Skeletal Morphology in Growing Children with Pierre Robin Sequence” was
published in the Cleft Palate-Craniofacial Journal in 2012. Drs. Oberoi and Shen were gracious
enough to provide this valuable data set for comparison in the present study.
Cross-sectional group analysis was used for measurements in two different age groups (4-8 years
old and 9-13 years old) for PRSMDO patients. These values were compared and tested for
statistically significant differences using unpaired t-tests assuming unequal variances. The
groups had unequal sample sizes and some had been treated with MDO while others were
untreated. Measurements of the PRSMDO group and the PRS groups at both age groups were
compared to published normative measurements (McNamara, 1984). Two-tailed p-values of less
than or equal to .05 were reported as statistically significant.
28
V.Results
V.1.Airway
Respiratory distress or respiratory failure in all 12 patients had resolved following MDO,
confirmed by PSG when compared to normative values. See table 4. Standard research
definitions for OSA severity as described by Katz et al. were used to classify patients as mild (1
to >5 AHI/hour), moderate (5 to >10 AHI/hour), or severe OSA (> or = 10 AHI/hour) (2008).
The mean AHI was 2.37 (range 0-14). One patient was classified as severe residual OSA, one
patient had moderate residual OSA and the remaining patients had mild or no residual OSA. See
table 6. However, all patients’ surgical treatment was considered successful in providing
sufficient relief of airway obstruction. There was no need for further treatment and all residual
OSA could be managed conservatively.
V.2. Craniofacial Growth
There were several skeletal growth differences observed between this PRSMDO sample and
untreated PRS patients described in the literature. There was a statistically significant increase in
gonial angles (ML/RL) of the PRSMDO patients compared to untreated PRS patients, which
indicates a vertical change in the direction of mandibular growth. The mandibular body ramus
length (Ar-GO) was significantly shorter and mandibular body (Go-Gn) was significantly longer
in PRSMDO patients. Chin prominence (SN-Pg) was greater in PRSMDO patients.
Maxillomandibular sagittal relationship (ANB) had a statistically significant closer
approximation. Upper face height (N-ANS) and lower face height (ANS-Gn) were both shorter
with statistical significance, as were the maxillary length (Co-A) and mandibular length (Co-Gn).
29
All other measurements showed no statistical significance. See tables 6-19. Sn-Go-Gn was
expected to be different, moving toward a high angle, open bite, dolichocephalic profile.
All 12 PRSMDO patients were analyzed using Bjork’s polygon analysis. Bjork’s polygon
utilizes 3 angles and the lengths of the sides of the polygon comprised of connecting the points
N-S-Ar-Go-Gn to make inferences about the possible nature of facial growth (Bjork, 1948;
Ghom, 2009). All patients maintained a class I or super class I skeletal and dental relationship.
Five patients presented with ideal overjet and overbite relationship of their incisors (Figure 10), 2
presented with anterior open bites (Figure 11), and 5 patients presented with edge-to-edge or
slight negative overjet (Figure 12).
When comparing the PRSMDO patients to published norms by Bjork some significant
observations were noted (1947). The sum of angles was equal to 407.73°, which lies outside the
range of normal (396 +/- 6), indicating a clockwise or vertical growth rotation. See figure 13.
The saddle angle of PRSMDO patients is decreased compared to the norm (124° +/-5° vs.
199.96° +/- 9.34°) which indicates mandibular prognathism (figure 14). In addition, the anterior
cranial base (S-N) is significantly shorter in the PRSMDO patients compared to the norm (59.78°
+/- 6.04° vs. 73° +/-3°), giving these patients, cephalometrically, a lengthened mandibular
length. In a normal (non-PRS) patient, the anterior cranial base (S-N) should be equal to the
mandibular length (Go-Gn). However in the PRSMDO patients, the ratio of the anterior cranial
base to mandibular length is not equal. The anterior cranial base (59.78° +/- 6.04°) is greater than
the mandibular length (51.96° +/- 5.97°). This may explain why although the increased saddle
angle would indicate mandibular prognathism in PRSMDO they actually present with an
orthognathic class I skeletal relationship. In other words it appears that even after lengthening of
the mandible with distraction osteogenesis the mandibular length remains intrinsically smaller
30
but the diminished saddle angle and shortened cranial base compensate and allow for the position
of the mandible to exist in a class I skeletal relationship.
31
VI. Discussion
Severe micrognathia, as seen in Pierre Robin sequence, is often accompanied by obstructive
apnea. When conservative measures such as prone positioning, supplemental oxygen, and
tongue-lip adhesion are insufficient, surgical intervention is required. Mandibular distraction
osteogenesis addresses the primary skeletal deformity of a hypoplastic mandible to alleviate
respiratory distress, without the morbidity associated with tracheostomy. The anterior movement
of the mandible results in an increased upper airway volume.
VI.1. Airway
Polysomnography is the standard for establishing the diagnosis of obstructive sleep apnea (OSA)
in infants, children, and adults. See table 2. Polysomnography provides the following measures:
sleep state (≥2 EEG leads), electrooculogram (right and left), submental electromyelogram
(EMG), airflow at nose and mouth (thermistor, capnography, or mask and pneumotachygraph),
chest and abdominal wall motion (impedance or inductance plethysmography),
electrocardiogram (preferably with R-R interval derivation technology), pulse oximetry
(including a pulse waveform channel), end-tidal carbon dioxide (sidestream or mainstream
infrared sensor), video camera monitor with sound montage (analog or digital), transcutaneous
oxygen and carbon dioxide tensions (in infants and children < 8 y). Multiple physiologic
parameters are monitored during polysomnography. See table 3. Generally, electrooculography,
chin and leg surface electromyography (EMG), and at least 2 EEG channels are included to
confirm sleep and assess sleep architecture. Breathing is assessed using nasal/oral airflow
sensors, pulse oximetry, and end-tidal (ET) CO
2
measurements monitoring, and by placing piezo
crystal belts across the chest and abdomen to detect respiratory efforts. At least one ECG channel
is necessary to determine heart rate and rhythm. Occasionally, other channels are incorporated
32
into the study as needed. These might include additional EEG leads to better detect seizure
activity, esophageal pH measurements, or transcutaneous carbon dioxide monitoring.
Polysomnographic normal standards differ between children and adults. In the pediatric age
range, abnormalities include oxygen desaturation under 92%, more than one obstructive apnea
per hour, and elevations of ET CO
2
measurements of more than 50 mm Hg for more than 9% of
sleep time or a peak level of greater than 53 mm Hg.
Respiratory scoring in children is also quite different from that of adults. Pediatric scoring must
be used for children ≤ 12 years of age. As there is a scarcity of data for adolescents, the use of
pediatric scoring criteria for teenagers between 13–17 years of age is optional. Small studies that
incorporated adolescents indicate that their breathing patterns during sleep are similar to that of
younger children, and hence, the use of pediatric scoring criteria would be appropriate (Catano et
al., 2001; Yates et al., 2002; Grigg-Damberger, 2012; Katz et al., 2012). Adult criteria are used
for patients ≥ 18 years of age. In adults, apneas and hypopneas are only scored if they are ≥ 10
seconds duration. Children have a faster respiratory rate than adults, and a lower functional
residual capacity. They are, therefore, more likely to desaturate and suffer physiologic
consequences from brief apneas. Because of this, obstructive apneas and hypopneas are scored if
they are at least 2 breaths, even if they are < 10 seconds duration (Suri et al., 2010). Hypopneas
are defined as a 50% reduction in airflow associated with either arousal or ≥ 3% desaturation.
Obstructive events in children occur primarily during rapid eye movement (REM) sleep (Iber et
al., 2007). Thus, if sufficient REM sleep is not obtained during a polysomnogram, the degree of
OSAS is likely to be underestimated.
Children tend to have clinical complications of obstructive sleep apnea syndrome with a much
lower apnea hypopnea index (AHI) than adults, and many centers will treat children with an AHI
33
in the 2–5/hr range. The AHI is the number of apneas of hypopneas recorded during the study
per hour of sleep and is expressed as the number of events per hour. An AHI of 10/hr, though
mild for adult patients, is considered to be moderately severe in children. Table 4 outlines the
normal polysomnographic values for children aged 1-18.
VI.2. Skeletal Changes
In PRS patients, micrognathia can lead to clefting of the palate. This requires repair, which can
result in scar tissue formation. The fibrosis of palatal tissues restricts the expression of the
maxilla’s natural genetic growth potential, causing the maxilla to be hypoplastic. This is
proportionate to the micrognathic mandible with which it is in occlusion. With distraction there
is a vertical component to the growth leading the maxillomandibular complex to rotate in a
clockwise fashion. This can lead to vertical maxillary excess, excess gingival display, and
increased vertical height. Considering the hypoplasia of the maxilla and mandible, dental
crowding is expected. Hypodontia in the posterior segment is a possible complication when the
distraction device is fixated to the mandible in line with developing tooth buds.
With MDO in this patient population, it has been observed that gonial angle increases, ramus
height is significantly shorter and mandibular body length is significantly longer. Posnick and
Reyneke both suggest that nasion, A-point and B-point should be roughly in a vertical line to
achieve ideal facial skeletal and soft tissue esthetics (2007, 2011). In this patient population,
mandibular distraction improves individual cephalometric measurements, but facial harmony and
alignment of those hard and soft tissue points as in non-PRS patients is not achieved. Patients
that have undergone MDO will not have nasion, A-point, and B-point in line and parallel to true
vertical line unless they have orthognathic surgery after skeletal maturation is complete.
Mandibular distraction is beneficial in lengthening the mandibular body, but the final result may
34
not be esthetically ideal. Due to an increase in gonial angle and steepening of the occlusal plane,
class II skeletal relationships are not always corrected. These patients typically present with a
dolichocephalic facial type warranting two-jaw orthognathic surgery to advance the mandible and
counter-clockwise rotate the occlusal plane. The medical management of the airway patency was
maintained in all 12 PRSMDO patients. From an airway management point of view, the MDO
procedure was successful long term.
It should be noted that the maxillomandibular discrepancy was significantly less in the MDOPRS
patients as compared to untreated PRS patients, and all 12 patients maintained a class I or super
class I dental occlusion. Daskalogiannakis et al. concluded that proportion of maxilla to affected
mandible does not improve after age 5 in cleft patients (2011). According to their study, a
micrognathic patient, if left uncorrected will have an equally constricted maxilla which will have
implications for dental crowding beginning in the mixed dentition. Either this is due to late catch
up growth described by Daskalogiannakis, or more likely, the amount of distraction during the
infant stage, which placed the infant in a significant class III skeletal relationship in anticipation
of further growth, was sufficient and allowed the patients to present at the time of our study with
a class I or super class I skeletal relationship.
It should be noted that the literature had previously described that PRS patients have a tendency
toward a more vertical growth direction (Herman et al., 2003). The current study was able to
identify some changes in direction of growth potentially caused by the early intervention with
MDO. These include an increased gonial angle and a more vertical growth pattern than that of
the untreated PRS patient. The increased gonial angles and even greater increase in vertical
growth rotation of the PRSMDO compared to untreated PRS patients suggests that these changes
can be caused by early intervention with MDO. However, these changes in the direction of
35
growth cannot be fully appreciated in our age population because the age of these patients is
before the peak of mandibular growth. Therefore further follow-up of these patients is needed to
determine if growth will continue in this increased vertical pattern.
Of interest is the significantly shorter anterior cranial base, upper and lower facial height and
overall maxillary and mandibular length. These differences may indicate that the faces of
MDOPRS patients are intrinsically smaller. Beginning with the cranial base this pattern radiates
outward, affecting the skeletal midface and the maxillomandibular complex.
36
VII. Conclusion
The candidates for early intervention with MDO represent the most severe micrognathia cases of
the PRS spectrum. Lengthening of the mandible by distraction osteogenesis is an effective
surgical treatment alternative to tracheostomy in neonates and infants with micrognathia-related
obstructive sleep apnea. There is less morbidity and mortality associated with this treatment
modality and the result is a positive change in respiration and improvement in
maxillomandibular relationship. The growth trends in MDO-treated Pierre Robin sequence
patients differed from that of untreated PRS samples. Further follow-up of these patients is
needed to determine if the growth trends post-distraction will continue through skeletal maturity,
and if these patients will require non-elective orthognathic surgery and secondary reconstructive
procedures in the future.
37
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44
VIII. Appendix of Figures and Tables
Figure 1. Infant with Pierre Robin sequence Micrognathia
Figure 2. Sample cephalograms of patient with craniofacial microsomia treated with MDO
Figure set 3. Modified Pruzansky Classification System
(From Grabb and Smith’s Plastic Surgery 6
th
ed., 2007)
Type I Type IIa Type IIa 3-D
Type IIb Type IIb 3-D Type III
45
Type III Type III 3-D
Figure 4: Sample Cephalogram of patient with Treacher Collins
46
Figure 5. Sample Cephalogram of patient with Treacher Collins MDO
Figure 6: Polysomnogram Sample of 4 Year Old with OSA
Hypnogram from a 4 year old girl with OSAS. Note that pediatric OSAS occurs primarily in
REM sleep (bold bars), with sleep architecture preserved.
Abbreviations: Stage: W: wake, 1: stage N1, 2: stage N2, 3: stage N3; A/H type: Apnea/
hypopnea type: OA: obstructive apnea, CA: central apnea, MA: mixed apnea, H: hypopnea;
SAO2: oxygen saturation (%); CAP: capnography (mm Hg).
47
Figure 7. Mandibular Distraction Osteogenesis Internal Device
Figure 8. Bjork ’s Polygon showing landmarks of interest
48
Figure 9 (.1-.12): Lateral Cephalograms with Bjork Tracings of PRS patient who received MDO
Patient #1 Patient #1
Patient #2 Patient #2
Patient #3 Patient #3
49
Patient #4 Patient #4
Patient #5 Patient #5
Patient #6 Patient #6
50
Patient #7 Patient #7
Patient #8 Patient# 8
Patient #9 Patient #9
51
Patient #10 Patient #10
Patient #11 Patient #11
Patient #12 Patient #12
52
Figure 10: Sample Cephalogram of Class I skeletal relationship with ideal OJ and OB
incisor relationship n=5
A
B
Figure 11: Sample Cephalogram of Class I skeletal relationship with anterior open bite
incisor relationship n=2
A
53
Figure 12: Sample Cephalogram of Super Class I skeletal relationship with negative overjet
incisor relationship n=5
A
B
Figure 13: Sample Bjork Polygon of PRSMDO patient w/sum of angles exceeding the norm
54
Length (mm)
Figure 14: Diminished saddle angle (decrement 10°)
Figure 15: Average Mandibular lengths of PRSMDO, PRS and the norm
120
116.6
103
100
80
95.6
93.3
81.5
103.1
PRSMDO
PRS
Normal
60
Ages 4-8 Yrs Ages 9-13 Yrs
55
length (mm)
Angle (degrees)
Figure 16: Average Maxillary lengths of PRSMDO, PRS and the norm
100
95
84.7
86.3
90
85
74.25 76.2
80
75
69.95
65.6
70
65
PRSMDO
PRS
Normal
60
55
50
4-8 yrs 9-13 yrs
Figure 17: Average ANB for PRSMDO, PRS and the norm
6
5.2
5
5
4
4
4.6
3.6
3
2.3
2
PRSMDO
PRS
Normal
1
0
Ages 4-8 Yrs Ages 9-13 Yrs
56
Length (mm)
Figure 18: Average Maxilla/Mandible difference among PRSMDO, PRS and the norm
30
27
25
22.2
20 19
19.6
21.5
22.5
PRSMDO
PRS
Normal
15
10
Ages 4-8 Yrs Ages 9-13 Yrs
Table 1.Structures derived from the 1
st
and 2
nd
branchial arches and the otic capsule
First branchial arch Second branchial arch Otic capsule
Trigeminal nerve Facial nerve
Maxillary process, Maxilla,
Palatine bone, Zygoma,
Anterior part of auricle,
Mandible, Head of malleus,
Body of incus,
Tympanic bone
First branchial groove
External auditory meatus
Mandibular process
Eustachian tube
Middle ear cavity
Sphenomandibular ligament,
Tympanic membrane
Maxillary artery
Posterior part of auricle, long
process of incus, stapedial
superstructure, tympanic
surface, styloid process,
Lesser cornu of hyoid
Manubrium of malleus,
stylohyoid ligament
Hypoid artery, Stapedial
artery
Vestibular surface of stapes,
internal acoustic meatus,
Inner ear
57
Table 2: Medical Conditions Associated with OSA in Children
(from Principles and practices of sleep medicine, 2011)
Table 3: Normal Parameters for Sleep Gas Exchange and Gas Exchange in Children
(from Principles and practices of sleep medicine, 2011)
58
Table 4: Recommended Normative Polysomnographic Values for Children Aged 1-18
Years.
Table 5: Sample Characteristics
No. of Children
With
Cephalograms at
T1 (4-8 y; mean
~6y)
No. of Children
With
Cephalogram at
T2 (9-13 y;
mean~11y)
No. of Children
With
Cephalogram at
T1 and T2
Total No. of
Children
PRSMDO group 6 6 0 12
PRS group 5 3 5 13
Table 6: Polysomnography of PRSMDO Patients.
Patient # Pre-op AHI Post-op AHI Most Recent
AHI
Age (Years) at Most
Recent PSG
1 4.5 0.75 0.7 2.33
2 Respiratory Failure 2.6 0 0.17
3 Respiratory Failure 0.95 0.1 6
4 Respiratory Failure 1.5 1.5 0.25
5 18.7 5 0.6 5
6 Respiratory Failure 13.9 14 3
7 Respiratory Failure 0 0 0.25
8 Respiratory Failure 0 0 3
9 25 6.9 6.9 0.5
10 100 7.9 0.4 2
11 Respiratory Failure 0.9 0.9 10.33
12 Respiratory Failure 3.3 3.3 1
MEAN 4.51 2.37 2.82
SD 4.51 3.99 3.03
59
Apneas per hour of sleep
Table 7: PRSMDO AHI changes long-term
14
12
10
8
6
Post-op AHI
Most Recent AHI
4
2
0
1 2 3 4 5 6 7 8 9 10 11 12
Patient #s
60
Table 8: Patient #2 Bjork Analysis and Wiggle Diagram
61
Table 9: Patient #2 Bjork Analysis and Wiggle Diagram
62
Table 10: Patient #3 Bjork Analysis and Wiggle Diagram
63
Table 11. Patient #4 Bjork Analysis and Wiggle Diagram
64
Table 12. Patient #5 Bjork Analysis and Wiggle Diagram
65
Table 13. Patient #6 Bjork Analysis and Wiggle Diagram
66
Table 14. Patient #7 Bjork Analysis and Wiggle Diagram
67
Table 15. Patient #8 Bjork Analysis and Wiggle Diagram
68
Table 16. Patient #9 Bjork Analysis and Wiggle Diagram
69
Table 17. Patient #10 Bjork Analysis and Wiggle Diagram
70
Table 18. Patient #11 Bjork Analysis and Wiggle Diagram
71
Table 19. Patient #12 Bjork Analysis and Wiggle Diagram
72
Table 20: Bjork Analysis of PRSMDO patients
PT # 1 2 3 4 5 6 7 8 9 10 11 12 MEA
N
SD
AGE 8.58 6.42 5.67 9 6.92 9.08 2.25 7.25 6.25 7 10.3
3
9 7.31 2.1
3
SADDLE/S
ELL
A ANGLE
(SN- AR)
(º)
143.
7
112.
5
118.
1
117.
2
121.
2
113.
6
124.
6
112.
4
126 108.
5
116.
5
125.
3
119.9
7
9.3
4
ARTICUL
AR
ANGLE (º)
139.
1
153.
2
144.
9
140.
5
143.
6
145.
9
140.
9
152.
1
134.
3
154.
9
147.
1
149.
4
145.4
9
6.2
2
GONIAL/
JAW
ANGLE
(AR- GO-
ME) (º)
153 145.
9
138.
9
150.
8
139.
8
136.
4
132.
2
140.
7
151.
4
146.
4
142.
3
129.
5
142.2
8
7.5
1
CHIN
ANGLE
(ID-PG-
MP) (º)
66.3 66.9 64.5 62.5 72.1 63.5 75.7 69.3 58.3 71 58.9 74.3 66.94 5.7
0
ANTE
RIOR
CRA
NIAL
BAS
E
(SN)
(MM)
62.7 59 52.2 58.2 59.1 60.2 59 77.2 58.8 57.6 57.7 55.6 59.78 6.0
4
POSTERIO
R
CRANI
AL
BASE
(S-AR)
(MM)
20.6 27.6 33.3 28.3 31.6 31 29.8 40.2 29.4 31.5 30.7 36.9 30.91 4.8
3
RAMUS
HEIGHT
(AR-
GO)
(MM)
36.3 31.2 31.9 24.8 31.4 31.5 30 37.3 27.5 25.3 34.7 24.2 30.51 4.3
7
LENGTH
OF
MAND
BASE
(GO-
PG)(MM)
50.6 50.8 53.1 45.8 49.3 47.9 55.3 65.9 52.7 43.3 50.3 58.5 51.96 5.9
7
UPPER
FACE
HEIGH
T (N-
ANS)
(MM)
47.8 42 42.8 40.2 42.9 39.3 38 53.2 46.6 41.6 47.7 45.6 43.98 4.3
4
LOWER
FACE
HEI
GHT
(AN
S-
GN)
(MM
)
83 63.8 61.8 54.5 61.9 58.7 58.6 82.6 60.9 62.2 59.8 59.4 63.93 9.1
2
TOTAL
FACE
HEIGH
T (N-
GN)
(MM)
129.
6
105.
5
102.
9
93.9 103.
2
97.7 96.1 134.
9
107.
1
101.
7
107.
5
104.
7
107.0
7
12.5
5
CRANIO-
MD
BASE
(MP-SN)
(º)
75.8 51.7 41.9 48.5 44.5 35.9 37.7 45.2 51.7 49.9 45.9 44.2 47.74 10.1
4
CRANIO-
MX
BASE/SN-
12.3 12.5 21.2 16.6 13.3 4 9.4 8.8 12.9 12.2 17.8 18.5 13.29 4.7
2
73
Table 20 continued: Bjork Analysis of PRSMDO patients
PALATAL
PLANE (º)
MX BASE-
OCC
PLANE (PP-
OP) (º)
32 15.9 9.4 11.6 11 16 15.7 10.6 14.6 * * 8.1 14.4
9
6.7
9
MAND
PLANE TO
OCC PLANE
(º)
31.5 23.3 11.3 20.4 20.2 15.8 12.6 25.8 24.3 * * 17.6 20.2
8
6.2
2
PALATAL-
MAND
ANGLE
(PP- MP) (º)
63.5 39.2 20.7 31.9 31.2 31.8 28.3 36.4 38.9 37.7 28.2 25.7 34.4
6
10.7
3
SNA (º) 63.6 77.3 85 74.1 79 82.8 77.4 79.5 72.7 82.1 74 72.7 76.6
8
5.7
8
SNB (º) 58 72.3 78.1 69 73.4 79.8 76 77.1 74 74.2 74.3 71.6 73.1
5
5.6
0
SNP (º) 56.2 72 79.1 70.6 71.8 80.8 75.9 76 73.4 73.5 75.5 72.2 73.0
8
6.1
3
ANB (º) 5.6 4.9 6.9 5.1 5.6 3 1.3 2.4 -1.3 7.9 -0.3 1.2 3.5
3
2.9
1
(B-AR) -
(A-
AR)(MM)
14.6 8.2 6.6 2.6 2.9 6.9 8.4 11.5 13 2.4 13.7 8.2 8.2
5
4.2
9
U1 - OCC
PLANE (º)
50 60.6 72.6 69.4 71.1 54.2 62.6 70 57.7 * * 45.5 61.3
7
9.4
7
U1 - PALATAL
PLANE/M
X BASE (º)
98 103.
5
98 99 98 109.
8
101.
8
99.4 107.
7
109 109.
9
126.
4
105.
0
4
8.2
9
L1 - OCC
PLANE (º)
82.1 74.3 86 81.6 71.9 83.1 78 79.3 84 * * 67.7 78.
8
5.8
5
L1 - MP
(LADH)
(MM)
37.4 35.6 31.3 30.4 34.6 33.9 33.9 48.1 33 33.4 31.5 32.8 34.6
6
4.6
5
INTERINCISA
L ANGLE
(U1- L1) (º)
132.
1
134.
8
158.
5
151 143 137.
3
140.
6
149.
3
141.
6
134.
8
143.
6
113.
2
139.
9
8
11.3
5
WITS
APPRAISA
L (MM)
-5.9 -2.9 -5.8 -0.5 -0.1 -3.5 -6 -3.4 -8.3 * * -4.3 -
4.0
7
2.5
5
*Insufficient landmarks
74
Table 21 Cephalometric Measurements from UCSF Cranio Analysis for PRSMDO patients
Patient # 1 2 3 4 5 6 7 8 9 10 11 12 Mean StdDev
Measuremen
ts
Cranial
base
measurem
ents
Anterior
cranial base
(SN), mm
62.7
59
52.2
58.2
59.1
60.2
59
77.2
59.1
46.4
57.7
55.4
58.9
7.17578
Sagittal
maxillary
measureme
nts
SNA 63.6 77.3 85 74.1 79.0 82.8 77.4 79.5 72.7 81.9 74 80.5 77.3 5.710092
Maxillary
length
(Co-A),
mm
64.9
59.5
69.5
61.2
68.5
69.9
66.9
80.7
68.9
52.8
60.7
77.2
66.7
7.669198
Sagittal
Mand.mea
surements
SNB 58.0 72.3 78.1 69 73.4 79.8 76 77.1 74 72.9 74.3 71.4 73.0 5.60002
Mandibular
Length (Co-
Gn), mm
100.9
86.8
96.4
78.6
90
98
92.1
119
100
76.1
94.2
94.9
93.9
11.16092
Sagittal
jaw
relations
hips
ANB 5.6 4.9 6.9 5.1 5.6 3 1.3 2.4 -1.3 8.9 -0.3 9.1 4.3 3.332303
Maxilla/man
dibu lar
difference
(Co-
Gn/Co-A),
mm
27.0
22
21.4
13.6
18.2
23.3
21
30.5
24.5
17.5
27.8
15.3
21.8
5.134811
Wits
Appraisal,
mm
-5.9
-2.5
-5.8
-0.5
-0.1
-3.5
-6
-3.4
-8.5
**
**
5.5
-3.1
**
Vertical
maxillary and
mandibular
emasuremen
t
SN-MP 75.8 51.7 41.9 48.5 44.5 35.9 37.7 45.2 51.7 58.8 45.9 41.7 48.3 10.74541
Y-axis (SGn-
SN)
95.0 75.3 72 73.1 74.6 65.2 69.1 71.2 74.6 78.2 73.5 76.6 74.9 7.218327
Lower face
height (ANS-
Me), mm
74.7
59.1
59.5
52.4
60.5
56.4
56.6
78
56.7
52.8
55.9
56.7
59.9
8.057008
Dentoalve
olar
measurm
ents
75
Table 21Continued:Cephalometric Measurements from UCSF Cranio Analysis, PRSMDO patients
Upper incisor
to NA, mm
4.6
1.4
-5.6
0.3
-1.9
4.2
1
0.5
1.3
-0.4
2.6
-2
0.5
2.807134
Lower incisor
to NB, mm
5.4
5.5
3.7
2.2
3.2
2.5
3.4
3.6
0.9
4.7
2.5
6.2
3.7
1.557095
Interincisal
angle (U1-L1)
132.1
132
158.5
151.1
143
137
141
149
144
142
144
123
141
9.500283
Overjet, mm 5.1 1.8 -1.1 4.5 1.4 5.9 -0.9 0.3 -1.2 ** ** 3.1 1.9 **
Soft tissue
measurements
Upper lip to E-
plane, mm
7.5
6.6
-1.2
-1
0.09
2.4
1.1
2.6
-0.8
3.8
0
3
2.0
2.887393
Lower lip to E-
plane, mm
7.5
7.6
1.6
-1.1
0.02
4.4
2.5
7.7
-0.9
-4.5
2.4
2.6
2.5
3.83948
Nasolabial
angle (Col-Sn-UL)
109.4
93.9
111.4
120.4
122
104
102
87.9
109
111
111
92.8
106
10.53155
Chin angle (Id-
Pg-MP)
66.3
66.9
64.5
62.5
72.1
63.5
75.7
69.3
58.3
63.3
58.9
81.1
66.9
6.74083
76
Table 22: Cephalometric Measurements Comparing PRS and PRSMDO
PRS PRSMDO
Mean SD n Mean SD n P VALUE
AGE (YEARS, RANGE) 9.1
(4.1-16)
35 7.17
(2.25-10.33)
2.29 12
SS-N-SS (SNA) 77.5 4.1 35 76.4 5.56 12 0.47
ML/RL (GONIAL
ANGLE)
133.7 7 35 141.98 7.4 12 0.0001**
S-N-SM (SNB) 72.2 4.5 35 73.26 5.64 12 0.51
N-S-AR (SADDLE
ANGLE)
120.9 4.1 35 120.45 7.92 12 0.8
SS-N-SM (ANB) 5.2 2.6 35 3.13 2.57 12 0.021*
SN-PG (CHIN
PROMINENCE)
41.1 5.9 35 47.39 10.13 12 0.01**
AGE 5.33
(2-11)
4.93 3 7.17
(2.23-10.33)
2.29 12 0.17
GONIAL ANGLE (AR-
GO-ME) (°)
136.26 2.74 3 142.28 7.51 12 0.066
RAMUS HEIGHT( AR-
GO) (MM)
42 6.64 3 31.03 4.37 12 0.0002**
MANDIBLE BODY
LENGTH (GO-GN)
(MM)
48.83 8.2 3 62.4 7.16 12 0.045*
AGE (YEARS, RANGE) 11.7
(10.2-13)
0.7 34 9.25
(8.58-10.33)
0.75 4 0.0001**
ANTERIOR CRANIAL
BASE (SN) (MM)
69.51 2.91 34 59.05 3.08 4 0.0001**
UPPER FACE HEIGHT
N-ANS (MM)
51.8 3.33 34 45.1 4.01 4 0.0006**
LOWER FACE HEIGHT
ANS-ME (MM)
66.13 6.56 34 54 14.3 4 0.0008**
S-GO (MM) 66.24 6.04 34 62.73 4.124 4 0.27
MAXILLARY
LENGTHCO-A (MM)
83.64 5.06 34 68.18 7.1 4 0.0001**
77
Table 22 continued: Cephalometric Measurements Comparing PRS and PRSMDO
MANDIBULAR LENGTH CO-
GN (MM)
105.78 6.23 34 97 3.08 4 0.0092*
SNA (DEGREES) 76.53 3.75 34 73.28 7.86 4 0.16
SNB (DEGREES) 72.16 3.92 34 70.93 9.27 4 0.62
ANB (DEGREES) 4.39 2.97 34 2.38 2.54 4 0.2
WITS APPRAISAL (MM) 3.53 3.54 34 -4.57 1.22 4 0.0001**
A-N PERPENDICULAR (MM) -6.48 4.42 34 -7.53 3.92 4 0.65
PG-N PERPENDICULAR (MM) -18.73 7.88 34 -22.36 11.7 4 0.38
78
Table 23. Cephalometric Measurements Comparing Both Norms and PRSMDO to PRS at
ages 4 to 8 years
Measurements
PRS
Norm
Diff
P-
value
PRSMDO
Diff
p-
Value
Cranial base
measurements
Anterior cranial base
(SN), mm
64.1
71.9
7.8
0.005
58.8
-5.3
0.29
Sagittal maxillary
measurements
SNA 79.2 81.3 2.1 0.341 79.3 0.1 0.997
Maxillary length (Co-A),
mm
74.3
83.4
9.1
0.147
67.9
-6.4
0.16
Sagital mandibular
measurements
SNB 74.3 76.1 1.8 0.241 75.3 1 0.58
Mandibular Length (Co-
Gn), mm
93.3
103
9.7
0.024
95.6
2.3
0.74
Sagittal jaw relationships
ANB 5 5.2 0.2 0.839 4 1 0.57
Maxilla/mandibular
difference (Co-Gn/Co-A),
mm
19
19.6
-0.6
0.796
22.2
3.2
0.28
Wits Appraisal, mm
0.2
-1
-0.8
0.707
-5.9
-
6.1
0.046
Vertical maxillary and
mandibular measurement
SN-MP 41.6 36.2 5.4 0.002 46.6 5 0.178
79
Table 24. Cephalometric Measurements Comparing Both Norms and PRSMDO to PRS for
ages 9 to 13 years
Measurements PRS Norm Diff p-value PRSMDO Diff p-Value
Cranial base
measurements
Anterior cranial base
(SN),
mm
65
76.4
11.4
<.001
58.9
-6.1
0.02
Sagittal maxillary
measurements
SNA 78.5 78.5 0 0.123 75.4 -3.1 0.34
Maxillary length (Co-A),
mm
76.2 90.7 14.5 0.037 65.6 -10.6 0.009
Sagital mandibular
measurements
SNB 74.9 77.1 2.2 0.158 70.8 -4.1 0.019
Mandibular Length (Co-
Gn),
mm
103.1
116.6
13.5
0.002
81.5
-21.6
Sagittal jaw relationships
ANB 3.6 2.3 -1.3 0.782 4.6 1 0.026
Maxilla/mandibular
difference (Co-Gn/Co-A),
mm
27
22.5
-4.5
0.616
21.5
-5.5
0.082
Wits Appraisal, mm -1 -1 0 0.992 -1.7 -0.7 0.66
Vertical maxillary and mandibular
Measurement
SN-MP 41.7 34.4 -
7.
3
0.315 49.9 8.2 0.228
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Asset Metadata
Creator
Shamlian, Tamara N.
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Core Title
The long-term cephalometric and respiratory outcomes of mandibular distraction osteogenesis in infants with Pierre Robin sequence
School
School of Dentistry
Degree
Master of Science
Degree Program
Craniofacial Biology
Publication Date
05/01/2015
Defense Date
03/06/2015
Publisher
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Tag
airway obstruction,cephalometric,craniofacial,distraction osteogenesis,distraction surgery,Infants,long-term outcomes,mandibular distraction,mandibular length,maxillary length,neo-natal,OAI-PMH Harvest,obstructive apnea,orthognathic surgery,Pierre Robin sequence,polysomnography,respiratory,tracheostomy
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), Paine, Michael L. (
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Tags
airway obstruction
cephalometric
craniofacial
distraction osteogenesis
distraction surgery
long-term outcomes
mandibular distraction
mandibular length
maxillary length
neo-natal
obstructive apnea
orthognathic surgery
Pierre Robin sequence
polysomnography
respiratory
tracheostomy